In the science and technology in recent years, electricity is used in every part of technical fields in a form of such as a power source and an electrical signal. For conveying or transmitting them, cables and lead wires are used. As the raw material for such cables and wires, metals having high-conductivity, such as copper and silver, are used. Particularly, copper wires are very widely used from the viewpoint of cost.
The material denoted by simply “copper” is classified roughly into hard copper and soft copper (annealed copper) according to its molecular sequence. With this variety, a copper having desired property is used according to the usage purpose.
As the lead wires for electronic parts wiring, hard drawn copper wires are widely used. For example however, cables for electronic devices such as medical instruments, industrial robots, and notebook personal computers are used under such an environment as imposes the cables harsh external force, a composite-forces of bending, twisting, pulling, etc. Therefore, hard drawn copper wires are not suitable for such use and accordingly soft annealed copper wires are used.
The copper wire for such use is required to have a good conductivity (high conductivity) and a good bending durability, which are conflicting characteristics. To date, developments have been furthered for copper-material that has high conductivity with high durability against bending (see Patent Literatures 1 and 2).
For example, the invention defined in JP2002-363668 A (Patent Literature 1) relates to a conductor for a bending-durable cable having good properties in tensile strength, tensile elongation, and conductivity. Particularly, the literature describes a conductor of copper alloy wire for bending-durable cables using an oxygen free copper having a purity of 99.99 mass-% or more with addition of 0.05 to 0.70 mass-% of indium having a purity of 99.99 mass-% or more and 0.0001 to 0.003 mass-% of phosphorus having a purity of 99.9 mass-% or more.
The invention defined in JP09-256084 A (Patent Literature 2) relates to a bending-durable copper alloy wire, wherein the alloy includes 0.1 to 1.0 mass-% of indium and 0.01 to 0.1 mass-% of boron, and the balance is copper.
In general, a flat cable has such a construction: that multiple number of strip-like conductors, or so-called flat conductors, are arrayed flat on one common plane; that the array of the flat conductors is sandwiched between insulating films from the direction of the conductor-thickness, wherein one face of each of the insulating films has an adhesive layer and the films are applied so that each of the adhesive layers will be the inner face of the sandwich on the array of the conductors; and that the sandwich of the array of the flat conductors are hot-pressed by heated rollers applied over the insulating films so that the adhesive layers will be heat-bonded to form a laminated one body.
As the flat conductor, tin-plated or solder-plated annealed tough pitch copper or oxygen free copper is used. As examples of conductors for such kind of flat cables, JP63-617039 U (Patent Literature 3) describes an application of Cu—Sn alloy and JP11-111070 A (Patent Literature 4) describes a use of Cu—Ni—Si alloy.